The invention is based on a method for controlling the air speed in a sterilizing tunnel during its heating phase. Such sterilizing tunnels are used particularly to sterilize ampules, vials or the like in the pharmaceutical packaging industry. Filter elements for cleaning the air recirculated in the sterilizing tunnel are disposed in the sterilizing tunnels. So that the filter elements will on the one hand not be damaged but on the other hand will have their optimal cleaning effect and so that no particles will be torn out of the filter elements, it is necessary that the flow through the filter elements be at a certain air speed.
In a known method of this type, to attain a virtually constant air speed at various temperatures in the sterilizing tunnel during its heating phase, speed measuring instruments are used, which are coupled via a control unit to a fan, whose rpm is varied in accordance with the measured air speed. A disadvantage of this known method is that the air speed measuring instruments, because of the high temperatures attained in the sterilizing tunnel, such as 350xc2x0 C. at the end of the heating phase, have only a brief dwell time. Furthermore, because of the additional measuring instruments and control units, the known sterilizing tunnels are complicated in design. Measurement errors, for instance from soiling of the measuring devices, also go undetected, so that the sterilization process cannot be carried out reliably. This is because an incorrectly measured air speed also adjusts the rpm of the fan incorrectly, and so the filter elements fail to function optimally.
In another method, it is also known to set the fan rpm as constant, so that at 350xc2x0 C., for instance, it is 0.5 meters per second. To achieve this, however, an air speed of approximately 0.9 meters per second must be set when the sterilizing tunnel is cold. During the heating process, the initially set elevated air speed automatically decreases, because of the heating of the air, to the air speed required in the sterilization. At the beginning of the heating phase, however, because of the increased air speed and the accordingly large quantity of air, the filter elements disposed in the intake or outlet region of the fan are burdened heavily. Furthermore, the fan must be designed to be strong enough for the large quantity of air. Thus once again, this method entails relatively high effort and equipment expense.
The method of the invention for controlling the air speed in a sterilizing tunnel during its heating phase, has the advantage over the prior art that it works without additional air speed measuring instruments and at the same time is sufficiently precise, and the filter elements always function optimally. It follows from this that the fan or the filters need not be made more powerful, and that the sterilization process will function reliably. According to the invention, this is attained in that the fan rpm is varied in accordance with a predetermined function course.
Further advantages and advantageous refinements of the method of the invention for controlling the air speed in a sterilizing tunnel during its heating phase will become apparent from the claims and the description.